It is a known fact that it often takes several minutes from cold starting an engine until its cooling temperature has reached a level where the cab heating element provides any noticeable heating of the cab air. The larger the engine is, i.e. the more metal mass it has, the longer it takes to warm up from cold start. Engine efficiency also plays a roll in this context, meaning that a diesel engine generally takes longer to warm up than a gasoline engine. In the large truck diesels weighing up to about one ton, it will take up to ten minutes to achieve any noticeable warming of the air, so that, for example, the defroster system of the vehicle will begin to have any effect.
A known solution for achieving more rapid heating of the cab air and the engine coolant is to install an engine fuel-burning heater in the engine coolant system or the cab air system. Such units are available both for gasoline operation and diesel operation and are quite expensive.